In 2013 we continued our investigation into the role of regulatory T cells in the establishment and maintenance of chronic retroviral infections. Two papers in peer-reviewed journals were published describing our findings. 1. We discovered a novel subset of regulatory T cells that acted in an IL-2 independent, TNF alpha-dependent manner. We also found that the expansion of these regulatory T cells during retroviral infection was dependent not on virus infection per se, but rather on the CD8+ T cell response to the infection. This information opens new avenues for therapeutic interventions to modulate Treg responses. 2. Previous results from our lab demonstrated a strong role for regulatory T cells in suppressing immune responses to retroviral infection and allowing chronic infections to become established. Those studies primarily focused on suppression of CD8+ T cells. In collaboration with the Dittmer lab we showed this year that regulatory T cells also had suppressive effects on virus-specific CD4(+) T cell responses in vivo, affecting both their proliferation and their cytokine production. These findings highlight the important role of Tregs in retroviral infections and point to avenues of therapeutic intervention.